There is sometimes little or no difference in meaning between the simple past tense and the present perfect. Whether you choose to use one or the other is often dictated by the broader context (which is what Marius was telling you), and sometimes it simply has to do with how the speaker is looking at things when he/she says or writes the sentence.

And, as Marius also mentioned, we Americans tend to use the simple past tense somewhat more often than our British cousins do.